The subject matter disclosed herein relates to a slotted turbine airfoil. More particularly, aspects of the invention include a turbine airfoil having a moisture diverting slot for increasing the efficiency of a turbine stage including that airfoil.
In some stages of a turbine (e.g., the last stages of a low-pressure steam turbine section), the high speed and local wetness concentration of steam passing through these stages can erode the tip regions of rotating buckets, as well as the walls of the static nozzle airfoils. In order to combat the erosive effects of the steam in this region, manufacturers conventionally harden the bucket airfoil leading edges near the tip region, or shield the area with satellite strips. Another conventional approach involves removing accumulated water through water drainage arrangements in the nozzle outer sidewalls (or, endwalls), or through pressure and/or suction slots made in hollow static nozzle airfoils. This moisture is then collected in circumferential cavities between the turbine diaphragm and the turbine casing, which then drains to the condenser or other suitable pressure dump (or, chamber). However, both of these conventional approaches have respective downsides. In the case of hardening or shielding, the costs associated with such protection can be significant. In the case of conventional hollow airfoils with pressure or suction slots, theses airfoils and slots can be difficult to manufacture, and can be difficult to weld into the turbine diaphragm rings without causing distortion in the airfoil.